At present, a large quantity of electrical devices, such as videos, televisions, monitors, printers, photocopiers, etc., have an operating state mode known as waiting or ‘standby’ mode. Said state is similar for the user to a mode of disconnection of the apparatus, but, in fact, this is not the case, since the apparatus remains connected, consuming electrical energy.
Years ago, the disconnection of a piece of equipment literally meant this, the total disconnection of said equipment, and, therefore, that the consumption thereof was zero, or, in other words, the electricity meter did not record any consumption. Nowadays, however, the meters continue to record consumption, and the reason for this, among others, is the consumption of appliances in ‘standby’ mode’.
Increasingly frequently, electrical appliances are designed to be connected to electricity 24 hours a day, 7 days a week, and part of the electrical consumption of those appliances occurs when the apparatus is not really being used, but while the electrical appliance is in ‘standby’ mode’. In some products, such as printers or photocopiers, the ‘sleep’ or ‘standby’ mode entails an important saving. Even so, these appliances record the greatest consumption levels in ‘standby’ among office computer systems and other electrical appliances.
It is precisely the fact that the appliances are connected 24 hours a day which cause that, although the consumption in ‘standby’ of an apparatus is relatively low with respect to its consumption in normal or working mode, in absolute terms it is practically equivalent to it, since the number of hours that it consumes energy whilst it remains on ‘standby’ is much higher.
Various recent studies state that between 5 and 13 percent of electricity of domestic use consumed in developed countries may be attributed to appliances on ‘standby’, and it is forecast that this FIGURE will continue to increase due to the progressive increase in electrical appliances, computers and other electrical or electronic appliances, both in the home and in the office.
To avoid these consumptions arising from electrical appliances or other equipment provided with this ‘standby’ operating mode, there are solutions that in one or another way detect that the corresponding equipment is for a certain time in operating mode and after said time automatically disconnects. The disadvantages of this type of solutions are varied, but the difficulty in the measurement or calculation of the power which determines that a piece of equipment is in ‘standby’ mode’ is especially notable, and consequently, the reliability and the response in its operation, i.e. the non-disconnection or the undue disconnection of the apparatus.
Other more imaginative solutions try to detect the presence of a user which theoretically is using the apparatus. In the case of solutions which whereby, for example a presence sensor, detect the presence of a user, and which therefore serves as criteria to determine when an appliance should be disconnected. As is evident, these solutions have, among others, the problem of reliably detecting when said user is present, since on many occasions, prolonged periods with absence of movement by the user could be interpreted as the absence thereof, and therefore, an erroneous disconnection could be determined. In turn, this type of solution also has the reverse problem, i.e. that the user is present in the place where the appliances are found but is not using them, for which reason, no type of energy saving is achieved.
A known method to detect that a piece of equipment has gone into ‘standby’ consists of calculating or measuring the current power that it is consuming, and to make said measurement of the power, it is necessary to differentiate between linear and non-linear loads.
A linear load, such as, for example, a water heater, as it is supplied by a sinusoidal voltage, will also consume a sinusoidal current. In this type of loads, the power calculation is relatively easy since it only depends on RMS values of voltage and current and on the power factor. The calculation of the RMS value is very simple since, as they are sinusoidal waves, the RMS value is the peak value of the wave divided by the root of two.
A non-linear load, with a sinusoidal supply voltage, will not consume a sinusoidal current but a distorted wave. In this case the calculation of the power consumed by these loads is complex since as they are not sinusoidal waves the power is not proportional to the product of the RMS values of voltage and current and the power factor. In this case, neither does the RMS value of the wave correspond to the maximum value divided by the root of two. Electronic equipment is typically non-linear loads since they integrate power sources to convert the sinusoidal voltage of 230 Vrms of the grid in a DC voltage of values generally lower than 24 Vdc.
Since these detection solutions of the ‘standby’ mode’ operate both with linear loads and non-linear loads, but especially with the latter since it is the electronic equipment which incorporates low consumption modes, the method of power calculation cannot be based on the measurement of RMS values and the power factor. A more sophisticated method of calculation based on the average of the instantaneous value of the power throughout a defined time period should be used:
  P  =                    1        T            ⁢              ∫                                            v              ⁡                              (                t                )                                      ·                          i              ⁡                              (                t                )                                              ⁢                      ⅆ            t                                =                  1        N            ·                        ∑                      k            =            0                    N                ⁢                              v            ⁡                          (              k              )                                ·                      i            ⁡                          (              k              )                                          
This alternative ‘standby’ detection therefore demands instantaneous measurements of voltage and current as well as an important calculation power.
Another problem associated to this detection method is that it is necessary to define a power threshold value from which it is considered that a piece of equipment has entered in standby mode. The problem arises when we have to define this threshold value. On the one hand, the ‘standby’ consumption is quite different when we consider different types of appliances, for example, a television and a printer. On the other hand, furthermore, the ‘standby’ consumption is quite different within the same type of appliance according to their age, manufacturer, etc.
To all the above, we have to add that the circuits devoted to calculating power also have a residual consumption which in cases is quite considerable, which directly clashes with the objective for which they were created.